The synthesis of trimetallic nanoparticles represents an emerging strategy to maximize catalytic performances in noble metal-based catalysts. However, the controllable synthesis of trimetallic nanomaterials as well as the exact role played by the addition of a third metal in their composition over catalytic performances remains unclear. In this paper, we describe the synthesis of trimetallic nanoshells having AgAuPd, AgAuPt, and AgPdPt compositions by a sequential galvanic replacement reaction approach between Ag nanospheres as sacrificial templates and the corresponding metal precursors, i.e., AuCl4 (-) ((aq)), PdCl4 (2-) ((aq)), and/or PtCl6 (2-) ((aq)). In each of these systems, the composition could be systematically tuned by varying the molar ratios between Ag and each metal precursor. Nanoshells having Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 compositions were employed as model systems to investigate the effect of the addition of the third metal in their composition over the catalytic activities toward the 4-nitrophenol reduction. Our data demonstrate a significant enhancement in conversion percentages and thus the catalytic activities relative to the sum of their bimetallic counterparts, and this increase was dependent on the nature of the metals, corresponding to 826, 135, and 56 % for Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 nanoshells relative to their bimetallic analogs. The results presented herein demonstrate the strong correlation between catalytic activity and composition in multimetallic nanoshells, and that the incorporation of a third metal may represent a promising approach to boost catalytic activities for a variety of transformations.